树状数组小结

树状数组用于处理前缀和，单值修改多次询问

每次更新要向右进行更新sum一直到n为止 x += lowbit(x)

每次求和要从底开始向左加所有的sum直到0为止  x -= lowbit(x)

注意：数组要从1开始加

int lowbit(int x){
    return x&(-x);
}
ll sum(int x){
    ll sum=0;
    while(x > 0){
        sum = sum+c[x];
        x -= lowbit(x);
    }
    return sum;
}
void add(int x,int d){
    while(x <= n){
        c[x] = c[x]+d;
        x += lowbit(x);
    }
}